The present invention relates to heavy duty diesel (HDD) engines provided with exhaust gas recirculation (EGR) systems, and lubricating oil compositions providing improved performance in such engines. More particularly, the present invention relates to compression ignited internal combustion engines equipped with EGR systems in which intake air and/or exhaust gas recirculation streams are cooled below the dew point during operation (condensation mode), lubricated with a lubricating oil composition that provides acceptable performance over a drain period of at least 15,000 miles in such an engine.
Environmental concerns have led to continued efforts to reduce NOx emissions of compression ignited (diesel) internal combustion engines. The latest technology being used to reduce the NOx emissions of heavy duty diesel engines is known as exhaust gas recirculation or EGR. EGR reduces NOx emissions by introducing non-combustible components (exhaust gas) into the incoming air-fuel charge introduced into the engine combustion chamber. This reduces peak flame temperature and NOx generation. In addition to the simple dilution effect of the EGR, an even greater reduction in NOx emission is achieved by cooling the exhaust gas before it is returned to the engine. The cooler intake charge allows better filling of the cylinder, and thus, improved power generation. In addition, because the EGR components have higher specific heat values than the incoming air and fuel mixture, the EGR gas further cools the combustion mixture leading to greater power generation and better fuel economy at a fixed NOx generation level.
Diesel fuel contains sulfur. Even xe2x80x9clow-sulfurxe2x80x9d diesel fuel contains 300 to 400 ppm of sulfur. When the fuel is burned in the engine, this sulfur is converted to SOx. In addition, one of the major by-products of the combustion of a hydrocarbon fuel is water vapor. Therefore, the exhaust stream contains some level of NOx, SOx and water vapor. In the past, the presence of these substances has not been problematic because the exhaust gases remained extremely hot, and these components were exhausted in a dis-associated, gaseous state. However, when the engine is equipped with an EGR, and the EGR stream is cooled before it is returned to the engine, the NOx, SOx, water vapor mixture is cooled below the dew point, causing the water vapor to condense. This water reacts with the NOx and SOx components to form a mist of nitric and sulfuric acids in the EGR stream.
In the presence of these acids, it has been found that soot levels in lubricating oil compositions build rapidly, and that under said conditions, the kinematic viscosity (kv) of lubricating oil compositions increase to unacceptable levels, even in the presence of relatively small levels of soot (e.g., 3 wt. % soot). Because increased lubricant viscosity adversely affects performance, and can even cause engine failure, the use of an EGR system that operates in a condensing mode during at least a portion of the operating time, requires frequent lubricant replacement. API-CI-4 oils developed specifically for EGR equipped engines that operate in a condensing mode have been found to be unable to address this problem. It has also been found that simply adding additional dispersant is ineffective.
Therefore, it would be advantageous to identify lubricating oil compositions that better perform in heavy duty diesel engines equipped with EGR systems that operate in a condensing mode. Surprisingly, it has been found that by selecting certain additives, specifically certain viscosity modifiers and/or detergents, the rapid increase in lubricant viscosity associated with the use of engines provided with EGR systems that operate in a condensing mode can be ameliorated.
In accordance with a first aspect of the invention, there is provided a heavy duty diesel engine provided with an exhaust gas recirculation system in which intake air and/or exhaust gas recirculation streams are cooled to below the dew point for at least 10% of the time said engine is in operation, said engine being lubricated with a lubricating oil composition comprising a major amount of oil of lubricating viscosity, and a minor amount of one or more high molecular weight polymers comprising (i) copolymers of hydrogenated poly(monovinyl aromatic hydrocarbon) and poly (conjugated diene), wherein the hydrogenated poly(monovinyl aromatic hydrocarbon) segment comprises at least about 20 wt. % of the copolymer; (ii) olefin copolymers containing alkyl or aryl amine, or amide groups, nitrogen-containing heterocyclic groups or ester linkages and/or (iii) acrylate or alkylacrylate copolymer derivatives having dispersing groups.
In accordance with a second aspect of the invention, there is provided an engine, as described in the first aspect, wherein the lubricating oil composition further comprises a minor amount of one or more neutral and/overbased metal-containing detergents, wherein from about 50% to 100% of the one or more detergents are phenate and/or salicylate detergents.
In accordance with a third aspect of the invention, there is provided a heavy duty diesel engine provided with an exhaust gas recirculation system in which intake air and/or exhaust gas recirculation streams are cooled to below the dew point for at least 10% of the time said engine is in operation, said engine being lubricated with a lubricating oil composition comprising a major amount of oil of lubricating viscosity, and a minor amount of one or more neutral and/overbased metal-containing detergents, wherein from about 50% to 100% of the one or more detergents are phenate and/or salicylate detergents.
In accordance with a fourth aspect of the invention, there is provided an engine, as described in the third aspect, wherein the lubricating oil composition further comprises a minor amount of one or more high molecular weight polymers comprising (i) copolymers of hydrogenated poly(monovinyl aromatic hydrocarbon) and poly (conjugated diene), wherein the hydrogenated poly(monovinyl aromatic hydrocarbon) segment comprises at least about 20 wt. % of the copolymer; (ii) olefin copolymers containing alkyl or aryl amine, or amide groups, nitrogen-containing heterocylclic groups or ester linkages and/or (iii) acrylate or alkylacrylate copolymer derivatives having dispersing groups.
In accordance with a fifth aspect of the invention, there is provided a heavy duty diesel engine provided with an exhaust gas recirculation system in which intake air and/or exhaust gas recirculation streams are cooled to below the dew point for at least 10% of the time said engine is in operation, said engine being lubricated with a lubricating oil composition comprising a major amount of oil of lubricating viscosity, and a minor amount of one or more nitrogen-containing dispersants wherein greater than 50 wt. % of the dispersant nitrogen is non-basic.
In accordance with a sixth aspect of the invention, there is provided a method of operating a heavy duty diesel engine provided with an exhaust gas recirculation system in which intake air and/or exhaust gas recirculation streams are cooled to below the dew point for at least 10% of the time said engine is in operation, for at least 15,000 without a change of lubricating oil, which method comprises lubricating said engine with a lubricating oil composition comprising a major amount of oil of lubricating viscosity, and a minor amount of one or more high molecular weight polymers comprising (i) copolymers of hydrogenated poly(monovinyl aromatic hydrocarbon) and poly (conjugated diene), wherein the hydrogenated poly(monovinyl aromatic hydrocarbon) segment comprises at least about 20 wt. % of the copolymer; (ii) olefin copolymers containing alkyl or aryl amine, or amide groups, nitrogen-containing heterocylclic groups or ester linkages and/or (iii) acrylate or alkylacrylate copolymer derivatives having dispersing groups.
In accordance with a seventh aspect of the invention, there is provided a method, as in the sixth aspect, wherein the lubricating oil composition further comprises a minor amount of one or more neutral and/overbased metal-containing detergents, wherein from about 50% to 100% of the one or more detergents are phenate and/or salicylate detergents.
In accordance with a eighth aspect of the invention, there is provided a method of operating a heavy duty diesel engine provided with an exhaust gas recirculation system in which intake air and/or exhaust gas recirculation streams are cooled to below the dew point for at least 10% of the time said engine is in operation, for at least 15,000 without a change of lubricating oil, which method comprises lubricating said engine with a lubricating oil composition comprising a major amount of oil of lubricating viscosity, and a minor amount of one or more neutral and/overbased metal-containing detergents, wherein from about 50% to 100% of the one or more detergents are phenate and/or salicylate detergents.
In accordance with a ninth aspect of the invention, there is provided a method, as in the eighth aspect, wherein the lubricating oil composition further comprises a minor amount of one or more high molecular weight polymers comprising (i) copolymers of hydrogenated poly(monovinyl aromatic hydrocarbon) and poly (conjugated diene), wherein the hydrogenated poly(monovinyl aromatic hydrocarbon) segment comprises at least about 20 wt. % of the copolymer; (ii) olefin copolymers containing alkyl or aryl amine, or amide groups, nitrogen-containing heterocylclic groups or ester linkages and/or (iii) acrylate or alkylacrylate copolymer derivatives having dispersing groups.
In accordance with a tenth aspect of the invention, there is provided a method of operating a heavy duty diesel engine provided with an exhaust gas recirculation system in which intake air and/or exhaust gas recirculation streams are cooled to below the dew point for at least 10% of the time said engine is in operation, for at least 15,000 without a change of lubricating oil, which method comprises lubricating said engine with a lubricating oil composition comprising a major amount of oil of lubricating viscosity, and a minor amount of one or more nitrogen-containing dispersants wherein greater than 50 wt. % of the dispersant nitrogen is non-basic.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification.